summon: assemble user config files (aka dotfiles)

Although not tested on BSDs, Mac OS X, cygnus and the like, summon should work fine in any machine with GNU coreutils, findutils, diffutils, sed and bash installed. Feel free to send pull requests to increase compatibility and ease of deploy in systems other than GNU/Linux.

GNU Stow users: #summon shares basically the same concept with the key difference of not setting up links to directories to avoid non-tracked files inside it pollute your Git repository.